The use of double panes of glass and even triple panes of glass in order to provide insulation against heat and noise is well known. Such windows comprise two or more parallel panes of glass, usually mounted in an elastomeric material such as rubber, for example. That is to say, a strip of rubber material is disposed between the panes of glass at their edges, the rubber on the outside of said edges and below said edges. Means for compressing the rubber so as to seal the glass panes therein and prevent air from leaking into or out of the space between the panes is also provided.
In principal, the idea is extremely simple, however in order to be effective as an insulating device, it is necessary that the dead air space between the panes of glass is effectively sealed. Not only is the insulating value of such windows dependent upon the maintenance of the tight seal, but in addition, visibility also depends upon it. For if moisture condenses on the inner surface of the glass, or if a film of grease or dirt accumulates thereon, visibility will obviously be adversely affected if not altogether destroyed. And since it is often impractical to clean the surfaces, it is clear than an effective type seal is vital.
A number of attempts have been made from time to time to provide a satisfactory solution to the problem. These have in general involved the use of rubber sealing strips such as gaskets, with various means for compressing the gaskets against the panes. Experience, however, shows that such methods of this type as are presently known cannot provide sufficiently uniform pressure to provide an effective airtight seal.
In the case of a relatively loose storm window of the conventional type, some reduction in heat loss is achieved. There is no significant problem of condensation of moisture in such a case, because there is so much circulation between the ambient air and the space between the panes that no significant difference in humidity can exist for an extended period of time. However, the dirt problem is very severe, because of the entry of such large volumes of air causes a rapid deposition of a film of grease or dirt on the inner surfaces of the panes. At the end of a year or so, cleaning becomes imperative. If this is a physical impossibility, or substantially so, as in many cases for example in office buildings, or in non-slidable "picture windows," the results are extremely unsatisfactory. In such cases in fact, conventional storm windows really cannot be used; multipane insulating windows are required.
The use of a conventional rubber sealing strip in the normal way, that is, without special efforts to achieve uniform compression, substantially reduces the circulation between the ambient air and the space between the panes. One result is thus that the insulating effectiveness may reach a reasonably good level. Another is that the dirt may take roughly twice as long to accumulate between the panes; however, when it accumulates, the situation is just as unsatisfactory as the case of an ordinary storm window. In other respects, the situation may readily become intolerable, that is condensation of moisture between the panes. If humid air gets into the space between the panes, and the ambient temperature drops, condensation of moisture occurs between the panes and, since the circulation between the ambient air and the space between the panes is slow, the window may remain "fogged" for very substantial periods of time. Thus, in order to decrease the dirt problem, one finds that one has introduced condensation problems. All in all, therefore, one has not achieved a solution to the problem of maintaining good visibility conditions.
The next step in the evolution of insulating windows has been the introduction of factory sealed windows. These are the first true insulating windows. The space between the panes is truly evacuated and the insulating quality thereof is high. The dirt and condensation problem is minimized but still exists. The difficulties with these windows are the extremely high first cost, high insurance cost, and expense and difficulty of repair of replacement. The fact that factory fabricated insulating windows can be purchased only in certain specific standard sizes also places limitations in design, especially when curved windows are involved.
The fact that such expensive solutions have nevertheless found very substantial commercial success clearly indicates that the problem itself, that is obtaining good insulating quality without visibility impairment, is a pressing problem and a problem of great commercial importance, and one for which no obvious answer exists.
Thus, there remains a problem of providing a seal as good as presently possible only with factory fabricated insulating windows, which is at the same time inexpensive, readily adapted to any size or shape of window including curved windows, and which can be installed and repaired at the job site instead of requiring factory fabrication.
Of course, airtight seals are well known in technology, but the problem in connection with the insulating windows is to obtain a seal which is not only effective, but also extremely simple in design and installation, and extremely low in cost. Complicated construction may make excellent airtight seals for scientific and industrial apparatus, but have no place in the construction of buildings, or in vehicles such as automobiles, buses, trains, and airplanes, for simplicity is required.
The difficulties which must be overcome in the solution of this problem include the following:
1. Considerable force must be necessary to make a tight seal, but glass panes must not be broken nor stressed so that the glass panes might break upon a temperature change or additional stress.
2. It is not sufficient to provide an excessively large force at some points and inadequate force elsewhere. "Averages" are not what counts here, but rather a uniform seal around the peripheral inner edges of the adjacent surfaces of the glass panes.
3. Expansions and contractions caused by temperature variations with seasonal changes and by pressure variations with changes in elevation, for example during shipment, must be accounted for without causing breakage on one hand and/or air leakage on the other.